Inhibitor of New Growth 4 (ING 4) is a member of the Inhibitor of New Growth family of candidate tumour suppressor proteins of which 6 have been reported in humans (Garkavstev et al 1996). Loss of the ING4 gene has been reported in head and neck squamous cell carcinoma (Gunduz et al 2005) and in glioma (Garkavtsev et al 2004) and, although a number of different functions have been described for this protein, its precise mode of action is yet to be elucidated.
The ING gene products inhibit cell proliferation (Russell et al 2006, Campos et al., 2004, Shi and Gozani 2005) and their overexpression is associated with increased apoptosis (Nagashima et al., (2001). ING4 inhibition of cell proliferation is probably mediated by its binding to p53 and acetyltransferase p300 thus facilitating acetylation and activation of p53 (Shiseki et al. 2003). ING4 has been reported as a component of the HBO1 HAT complex required for normal cell cycle progression and the majority of histone H4 acetylation (Doyon et al, 2006) suggesting a role in chromatin remodelling and transcriptional regulation. The extensive loss of histone H4 acetylation during human cancer development strongly suggests a tumour suppressor role for ING4. ING4 has been shown to interact with the RelA subunit of NF-κB resulting in suppressed expression of angiogenesis-related genes such as IL-6, IL-8 and Cox-2 (Garkavtsev et al 2004) and its loss in glioma is associated with more aggressive tumour growth and vascularisation. Loss of tumour suppressor genes is a common feature of cancer progression. ING4 suppression in multiple myeloma cells in vitro resulted in increased expression of the pro-angiogenic IL-8 and osteopontin probably via increased activity of hypoxia inducible factor-1 (HIF-1), involved in up-regulating angiogenesis genes during hypoxia, and, in multiple myeloma patients, decreased levels of ING4 were associated with both high IL-8 production and microvascular density (Colla et al., 2007). ING4 repression of the HIF transcription factor, probably mediated via an interaction with HIF prolyl hydroxylase (HPH)-2, also involved in regulating angiogenesis genes, has also been reported (Ozer et al., 2005, Colla et al 2007).
Herpes Simplex Virus
The herpes simplex virus (HSV) genome comprises two covalently linked segments, designated long (L) and short (S). Each segment contains a unique sequence flanked by a pair of inverted terminal repeat sequences. The long repeat (RL or RL) and the short repeat (RS or RS) are distinct.
The HSV ICP34.5 (also γ34.5) gene, which has been extensively studied, has been sequenced in HSV-1 strains F and syn17+ and in HSV-2 strain HG52. One copy of the ICP34.5 gene is located within each of the RL repeat regions. Mutants inactivating both copies of the ICP34.5 gene (i.e. null mutants), e.g. HSV-1 strain 17 mutant 1716 (HSV 1716) or the mutants R3616 or R4009 in strain F, are known to lack neurovirulence, i.e. be avirulent (non-neurovirulent), and have utility as both gene delivery vectors or in the treatment of tumours by oncolysis. HSV-1 strain 17 mutant 1716 has a 759 bp deletion in each copy of the ICP34.5 gene located within the BamHI s restriction fragment of each RL repeat.
ICP34.5 null mutants such as HSV1716 are, in effect, first-generation oncolytic viruses. Most tumours exhibit individual characteristics and the ability of a broad spectrum first generation oncolytic virus to replicate in or provide an effective treatment for all tumour types is not guaranteed.
HSV 1716 is an oncolytic, non-neurovirulent HSV and is described in EP 0571410 and WO 92/13943. HSV 1716 has been deposited on 28 Jan. 1992 at the European Collection of Animal Cell Cultures, Vaccine Research and Production Laboratories, Public Health Laboratory Services, Porton Down, Salisbury, Wiltshire, SP4 0JG, United Kingdom under accession number V92012803 in accordance with the provisions of the Budapest Treaty on the International Recognition of the Deposit of Microorganisms for the Purposes of Patent Procedure (herein referred to as the ‘Budapest Treaty’).